1. Field of the Invention
The present invention relates to a water base ink set for ink-jet recording to be used for an ink-jet recording apparatus, the ink-jet recording apparatus including the same, and an ink-jet recording method.
2. Related Art
The ink-jet recording system is a recording system that inks of several colors, which constitute basic colors, are converted into minute droplets of several picoliters to several tens of picoliters by using an ink discharge method including, for example, the bubble method in which the ink is discharged from a minute nozzle in accordance with the action of bubbles generated by rapid heating, and the piezoelectric method in which the ink is discharged from a minute nozzle in accordance with the action of a piezoelectric element that is deformable depending on an applied voltage so that the minute droplets are selectively landed on a paper surface to form an image thereby.
The ink-jet recording system is excellent in that it is possible to reproduce colors approximate to those of the full color and form an image having no granular texture by highly accurately controlling the discharge of minute droplets, making it possible to realize a high text printing quality and a high photographic printing quality. However, in order to discharge the minute droplets with such a high degree of accuracy, it is required to use a highly accurate landing control technique based on the use of a sufficiently thin discharge nozzle. Further, it is required to remove any dust and impurities from the ink. Therefore, it is necessary that the water base ink for ink-jet recording is subjected to precision filtration, and sufficiently washed materials are used for all parts which make contact with the ink.
Most of typical full color ink-jet printers, which use the ink set composed of four colors of black, yellow, magenta, and cyan, use the ink containing the anionic dye in view of the coloring performance on the paper and the toxicity. However, the ink containing the anionic dye is insufficient in vividness, for example, especially in the case of the yellow color. It is demanded to obtain a more vivid color. In order to satisfy such a demand, it is preferable to use the cationic dye which is used for a marker pen or the like and which has vivid color development performance. On the other hand, each of single colors of the inks containing the cationic dyes is vivid. However, if the inks containing the cationic dyes are used for all inks, it is hard to say that they are suitable in view of the balance of colors. Therefore, in order to obtain an image which is vivid and which is excellent in color balance, it is preferable to use the ink containing the anionic dye and the ink containing the cationic dye in combination.
However, if the ink containing the anionic dye and the ink containing the cationic dye are used in combination, it is feared that the inks may be mixed with each other at the head discharge portion, and any insoluble inorganic salt may be produced, or any deposit may be formed due to the deposition or precipitation of the dye, because the head discharge portions for the respective colors of the ink-jet printer are arranged closely on an identical plane, and an identical wiper is used for the head discharge portions for the respective colors in order to clean the head discharge portions. The amount of produced deposit differs depending on, for example, the type and the concentration of the dye and the type and the concentration of the solvent. However, when the deposit is formed, then any clog-up occurs at the head discharge portion, and it is impossible to highly accurately control the discharge landing.
An ink-jet recording apparatus, which has only a single head, is provided with a single ink tank (or an ink cartridge) as well. Therefore, such an ink-jet recording apparatus can use only unicolor ink in ordinary cases. When the ink contained in the ink tank is consumed, it is necessary that the empty ink tank is exchanged with another tank filled with an ink. For example, when an ink contained in the tank filled with the anionic dye ink is exhausted, an user intends to use a cationic dye ink next time in some cases. In such a situation, it is necessary that the ink container, which was filled with the anionic dye ink, is detached from the ink-jet head, and the ink container, which is filled with the cationic dye ink, is attached thereto. During this process, if any anionic dye ink remains in the ink-jet head, it is feared that the anionic dye ink may be mixed with the cationic dye ink allowed to inflow into the head, and any insoluble inorganic salt may be produced, or any deposit may be formed due to the deposition or precipitation of the dye. The amount of produced deposit differs depending on, for example, the type and the concentration of the dye and the type and the concentration of the solvent. However, when the deposit is produced, then any clog-up occurs at the head filter and the nozzle, and it is impossible to highly accurately control the discharge landing.
In the case of the conventional method, when the problem as described above occurs, it has been necessary to perform a treatment such that the ink (or the ink tank) is exchanged after substituting the interior of the head with a washing solution or the like so that the anionic dye ink and the cationic dye ink are not mixed with each other. However, such a procedure takes a long period of time. Further, another problem arises such that large amounts of the ink and the washing solution or the like are required.
The present invention has been made in order to solve the problems involved in the conventional technique as described above, a first object of which is to provide a water base ink set for ink-jet recording which makes it possible to perform stable discharge without any occurrence of clog-up at the head discharge portion and which makes it possible to perform vivid recording with high reliability, high accuracy, and good color balance even when an ink containing an anionic dye and an ink containing a cationic dye are used in combination, and an ink-jet recording apparatus which accommodates the ink set.
A second object of the present invention is to provide an ink-jet recording method which makes it possible to perform stable discharge without any occurrence of clog-up at the head filter and the nozzle and which makes it possible to perform highly reliable and highly accurate recording even when an anionic dye ink and a cationic dye ink are used in combination.
According to a first aspect of the present invention, there is provided a water base ink set for ink-jet recording comprising:
a first ink which contains an anionic dye; and
a second ink which contains a cationic dye, wherein:
at least one of the first and second inks contains at least two glycols selected from the group consisting of diethylene glycol, triethylene glycol, and polyethylene glycol, polyvinyl pyrrolidone, and water.
In the water base ink set for ink-jet recording, the first ink and the second ink may have different colors. The ink set may further comprise third and fourth inks. In this case, the first to fourth inks may have mutually different colors. For example, the second ink may have a yellow color, and the first ink may have a black, magenta, or cyan color.
In the water base ink set for ink-jet recording, the first ink and the second ink may have an identical color. In this case, an user can select the ink containing the anionic dye and the ink containing the cationic dye depending on the information to be recorded, for example, depending on the combination of colors. The water base ink set for ink-jet recording may further comprise a third ink which contains an anionic dye having a color different from that of the first ink, and a fourth ink which contains a cationic dye having the same color as that of the third ink, wherein at least one of the third and fourth inks contains at least two glycols selected from the group consisting of diethylene glycol, triethylene glycol, and polyethylene glycol, polyvinyl pyrrolidone, and water. For example, the ink set may comprise the inks containing the anionic dyes having four colors of black, yellow, magenta, and cyan, and the inks containing the cationic dyes having four colors of black, yellow, magenta, and cyan. In this case, an user can appropriately select the ink containing the anionic dye and the ink containing the cationic dye for each of the colors.
According to a second aspect of the present invention, there is provided an ink-jet recording apparatus comprising:
an ink-jet head which ejects an ink onto a recording medium;
a carriage which holds the ink-jet head and which is movable opposingly with respect to the recording medium; and
an water base ink set for ink-jet recording, wherein:
the ink set comprises a first ink which contains an anionic dye, and a second ink which contains a cationic dye, and at least one of the first and second inks contains at least two glycols selected from the group consisting of diethylene glycol, triethylene glycol, and polyethylene glycol, polyvinyl pyrrolidone, and water.
In the ink set and the ink-jet recording apparatus of the present invention, the ink set may be in a form of ink cartridge which is connectable to the ink-jet head and which is replaceable. The first ink and the second ink may have different colors. Alternatively, the first ink and the second ink may have an identical color. The ink cartridges may be independent containers for the respective inks. Alternatively, the ink cartridge may be one container provided with compartments for accommodating the inks of different colors, respectively.
According to a third aspect of the present invention, there is provided an ink-jet recording method for discharging an ink contained in an ink container onto a recording medium from an ink-jet head, the method comprising:
performing recording by connecting, to the ink-jet head, one of a first ink container filled with a first ink containing an anionic dye and a second ink container filled with a second ink containing a cationic dye; and
performing recording by connecting, to the ink-jet head, the other of the first and second ink containers in place of the one ink container, wherein:
at least one of the first and second inks contains at least two glycols selected from the group consisting of diethylene glycol, triethylene glycol, and polyethylene glycol, polyvinyl pyrrolidone, and water. According to the ink-jet recording method of the present invention, the first ink can be replaced with the second ink contained in the second ink container, depending on the situation to perform the recording or after the first ink is exhausted. During this process, it is unnecessary to wash the ink flow passage in the head. The first ink and the second ink may have different colors. Alternatively, the first ink and the second ink may have an identical color.